The micro plate is a member wherein pluralities of wells, which can hold liquid, are arranged in a matrix form (row and column form). Known are, for example, 4 rows×6 columns (=24 wells), 6 rows×8 columns (=48 wells), 8 rows×12 columns (=96 wells), 12 rows×16 columns (=192 wells), and 16 rows×24 columns (=384 wells). The intervals between the individual wells in these micro plates tend to be normalized. In, for example, a micro plate having 96 wells, the row interval thereof, which is the distance in the column direction between the well centers of any one of the rows where some of the wells are arranged and those of the rows where wells adjacent to the wells in the column direction are arranged, and the column interval thereof, which is the distance in the row direction between those of any one of the columns where some of the wells are arranged and those of the columns where wells adjacent thereto in the row direction are arranged, are each 9 mm. In 384 wells, the well number of which is 4 times, the row interval and the column interval are each 4.5 mm.
When these micro plates are used to conduct simultaneous treatment operations, wherein plural kinds of solutions are used in parallel, the following dispensing device was used: a dispensing device wherein a single nozzle head equipped with nozzles the number of which is equal to the number of the individual wells in each of the micro plates or with dispensing tips fitted to the nozzles is used to insert the dispensing tips simultaneously into the individual wells in each of the micro plates and then solutions or suspensions to be handled so as to be equal to each other in kind or amount are sucked or discharged (Patent Document 1).
For example, in the case of causing plural kinds of reagents successively to react with many target substances extracted from many specimens etc. which are to be treated, thereby conducting a series of treatment operations, micro plates each having wells the number of which corresponds to the number of the specimens are prepared by the following number in order to hold, in advance, reagent solutions, specimens, or magnetic particle suspensions required for the treatment: a number corresponding to the number of steps required for the treatment process or the number of the required kinds of the reagents or the like. The dispensing device, which can cause the magnetic particles to be adsorbed on inner walls of the dispensing tips corresponding to nozzles, are used to transfer the magnetic particles successively to the individual wells in plurality of the micro plates, so as to suspend the particles in the wells, thereby causing reaction. These steps are successively performed, thereby conducting the treatment (Patent Documents 1 and 2).
Therefore, when the kinds of the reagents used in the treatment are increased, the number of the micro plates to be used increases since any one of the micro plates is assigned to each of the kinds. Thus, the area for the work increases. The moving distance of the nozzle head corresponds to the distance over which the nozzle head passes all the micro plates the number of which corresponds to the number of the kinds of the reagents or the like required for the treatment; therefore, when the number of the micro plates increases, the moving distance of the nozzle head increases. As a result, there remains a problem that it is feared that the treatment can neither be promptly nor effectively conducted.
When a liquid amount of about one hundred microliters to several hundreds of microliters is merely handled as in the prior art, the liquid amount can be sufficiently used by combining ordinary micro plates with the above-mentioned dispensing device. However, when the liquid amount to be handled is increased so that a liquid amount of about one thousand microliters to several thousands of microliters needs to be handled, it is necessary to increase the volume of each of the wells and further increase the volume of each of the dispensing tips. As a result, when the interval between the wells in the micro plates is normalized, the height of the micro plates increases and further the length of the dispensing tips in the axial direction thereof increases, so that the scale of the device is enlarged in the vertical direction. Thus, there remains a problem that is feared that the device may not be easily handled in order to attain the transfer of the nozzle head, or the like.
Furthermore, when the number of parallel treatment operations for handling specimens in parallel is increased, number of the wells in the micro plates increases: thus, necessity that the wells should be highly integrated increases. Accordingly, the individual nozzles need to be arranged closely to each other. Thus, the interval between the dispensing tips is made narrow so that the area occupied by each of the dispensing tips becomes narrow. As a result, there is caused a problem that is feared that functions to be adopted by the dispensing tips are unavoidably lowered.    [Patent Document 1:] International Publication WO 99/47267    [Patent Document 2:] Japanese Patent No. 3115501